Photoelectrochemical Properties of Thin Films of Zinc Porphyrin Derivatives with Pyridyl Group

The cathodic photocurrents of the film electrodes of ZnPyP3P(3) and ZnPyP3P(4), (PyP3P(n), 5-(2-, 3-, and 4-pyridyl)-10,15,20-triphenylporphyrin, where (n) denotes the position of free bond of pyridyl group), were almost four times larger than that of ZnTPP (TPP, 5,10,15,20-tetraphenylporphyrin) in 0.01 mol dm−3 quinhydrone aqueous solution at pH 5. On the other hand, the very small anodic photocurrent was observed with the film electrodes of ZnTPyP(3) and ZnTPyP(4) (TPyP(n),5,10,15,20-tetra(2-, 3-, and 4-pyridyl)porphyrin). The photoelectrochemical properties of ZnPyP3P(2) and ZnTPyP(2) were distinct from those of other structural isomers, but approximately similar to those of ZnTPP. The conductivities of ZnPyP3P(n) films were about three oders of magnitude larger than those of ZnTPP and ZnTPyP(n) films. It was found from the absorption and resonance Raman spectra that the pyridyl group in porphyrin coordinated to zinc in another porphyrin in the solid films as well as in toluene and dichloromethane solutions. The molecular arrangement of zinc porphyrin in the solid film probably influenced the photoelectrochemical properties and the conductivity.